Air filters such as those used in HVAC systems are fabricated with many different types of filter media. Depending upon the type of substance sought to be filtered or removed from air (e.g. particles, carbon monoxide, smoke, formaldehyde, organics, etc.), or the useful filter life required, different medias are selected. Examples of such medias are wet or dried laid paper, synthetic microfiber media, metal mesh, wet or dried laid fiberglass, activated carbon impregnated media, tack coated polyester and synthetic media impregnated with potassium permanganate.
One of the problems which arises as a result of selecting a specific filter media for a specific filtering requirement (e.g. filtering carbon monoxide) is that filtering performance for other requirements such as particulate filtration may be sacrificed. Accordingly, it would be desirable to combine different types of filter material layers to produce a filter media which will meet more than one filtering requirement. It would also be desirable to provide an arrangement for joining the filter material layers to allow both layers to be supported with a support grid.